The overall purpose of this proposal is to characterize the molecular genetic basis of the human immune response to the Ul-70kD small nuclear ribonucleoprotein (snRNP) autoantigen. This study is based upon our preliminary results in population immunogenetics studies, molecular genetic studies of major histocompatibility (MHC) genes, and cellular immunologic studies of human peripheral blood mononuclear cells stimulated with U1-RNP. In population immunogenetic studies we have found that the presence of autoantibodies against the Ul-70kD snRNP autoantigen is associated with the HLA-DR4 and HLA-DR2 phenotypes. Molecular genetic studies have further demonstrated that certain molecular subtypes of HLA-DRB genes are present among these patients. Based upon these results, we have hypothesized that the association of disease susceptibility to anti-Ul-70kD autoantibody-positive connective tissue disease is mediated, at least in part, by the presence of MHC restricted, T-helper cells which bind peptide fragments of the Ul-70kD antigen and present these to stimulate T cells. This system is of particular interest in that it is one of the few multisystemic human autoimmune diseases where a target of the immune response has been determined; the Ul70kD snRNP antigen has been molecularly cloned and is available in our laboratory as a recombinant fusion protein. We now propose to extend our findings by performing molecular immunogenetics studies among patients of diverse races to map the precise contribution of the MHC to disease susceptibility. To achieve this we will use the polymerase chain reaction (PCR), sequence specific oligonucleotide hybridizations, DNA cloning, and sequencing of both cloned and PCR amplified DNA. We also propose to generate Ul-70kD specific T cell clones and murine L-cell transfectants constructed with those HLA-DR or HLA-DQ alpha and beta chains genes which our immunogenetics and molecular genetics studies have suggested to be important in disease susceptibility. This in vitro analysis will allow for the dissection of the tripartite interaction between HLA, the Ul-70kD antigen and the T cell receptor.